arm64: dts: imx8mp: Add SoM compatible to i.MX8M Plus DHCOM PDK2

Add SoM compatible string into i.MX8MP DHCOM PDK2 compatible strings.
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@denx.de>
Cc: NXP Linux Team <linux-imx@nxp.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Shawn Guo <shawnguo@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mp-dhcom-pdk2.dts

@@ -16,7 +16,8 @@
 
 / {
 	model = "DH electronics i.MX8M Plus DHCOM Premium Developer Kit (2)";
-	compatible = "dh,imx8mp-dhcom-pdk2", "fsl,imx8mp";
+	compatible = "dh,imx8mp-dhcom-pdk2", "dh,imx8mp-dhcom-som",
+		     "fsl,imx8mp";
 
 	chosen {
 		stdout-path = &uart1;